Network Working Group M. Crispin
INTERNET DRAFT: IMAP UIDPLUS extension May 2005
Obsoletes: 2359
Document: internet-drafts/draft-crispin-imap-rfc2359bis-02.txt
Internet Message Access Protocol (IMAP) - UIDPLUS extension
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Abstract
The UIDPLUS extension of the Internet Message Access Protocol [IMAP]
provides a set of features intended to reduce the amount of time and
resources used by some client operations. The features in UIDPLUS
are primarily intended for disconnected-use clients.
Conventions Used in this Document
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are
to be interpreted as described in [KEYWORDS].
Introduction and Overview
The UIDPLUS extension is present in any IMAP server implementation
which returns "UIDPLUS" as one of the supported capabilities to the
CAPABILITY command.
The UIDPLUS extension defines an additional command. In addition,
this document recommends new status response codes in IMAP which
SHOULD be returned by all server implementations, regardless of
whether or not the UIDPLUS extension is implemented.
The added facilities of the features in UIDPLUS are optimizations;
clients can provide equivalent functionality, albeit less
efficiently, by using facilities in the base protocol.
1. Additional Commands
The following command definition is an extension to [IMAP] section6.4.
1.1 UID EXPUNGE Command
Arguments: message set
Data: untagged responses: EXPUNGE
Result: OK - expunge completed
NO - expunge failure (e.g., permission denied)
BAD - command unknown or arguments invalid
The UID EXPUNGE command permanently removes from the currently
selected mailbox all messages that both have the \Deleted flag set
and have a UID that is included in the specified message set. If
a message either does not have the \Deleted flag set or has a UID
that is not included in the specified message set, it is not
affected.
This command may be used to ensure that a replayed EXPUNGE command
does not remove any messages that have been marked as \Deleted
between the time that the user requested the expunge operation and
the time the server processes the command.
If the server does not support the UIDPLUS capability, the client
should fall back to using the STORE command to temporarily remove
the \Deleted flag from messages it does not want to remove. The
client could alternatively fall back to using the EXPUNGE command,
risking the unintended removal of some messages.
Example: C: A003 UID EXPUNGE 3000:3002
S: * 3 EXPUNGE
S: * 3 EXPUNGE
S: * 3 EXPUNGE
S: A003 OK UID EXPUNGE completed
2. Additional Response Codes
The following response codes are extensions to the response codes
defined in [IMAP] section 7.1. With limited exceptions, discussed
below, server implementations that advertise the UIDPLUS extension
SHOULD return these response codes.
In the case of a mailbox which has permissions set so that the client
can COPY or APPEND to the mailbox, but not SELECT or EXAMINE it, the
server SHOULD NOT send an APPENDUID or COPYUID response code as it
would disclose information about the mailbox.
In the case of a mailbox that has UIDNOTSTICKY status (as defined
below), the server MAY omit the APPENDUID or COPYUID response code as
it is not meaningful.
If the server does not return the APPENDUID or COPYUID response
codes, the client can discover this information by selecting the
destination mailbox. The location of messages placed in the
destination mailbox by COPY or APPEND can be determined by using
FETCH and/or SEARCH commands (e.g. for Message-ID or some unique
marker placed in the message in an APPEND).
APPENDUID
Followed by the UIDVALIDITY of the destination mailbox and the
UID assigned to the appended message in the destination mailbox,
indicates that the message has been appended to the destination
mailbox with that UID.
If the server also supports the [MULTIAPPEND] extension, then the
second value is a message set containing the UIDs assigned to the
appended messages, in the order they were transmitted in the
APPEND command. This message set may not contain extraneous UIDs
or the symbol "*".
UIDs are assigned strictly ascending in the mailbox (refer to
[IMAP], section 2.3.1.1) and UID ranges are as in [IMAP]; in
particular, note that a range of 12:10 is exactly equivalent to
10:12 and refers to the sequence 10,11,12.
This response code is returned in a tagged OK response to the
APPEND command.
COPYUID
Followed by the UIDVALIDITY of the destination mailbox, a message
set containing the UIDs of the message(s) in the source mailbox
which were copied to the destination mailbox, and a message set
containing the UIDs assigned to the copied message(s) in the
destination mailbox, indicates that the message(s) have been
copied to the destination mailbox with the stated UID(s).
The source message set is in the order the message(s) were copied;
the destination message set corresponds to the source message set
and is in the same order. Neither of the message sets may contain
extraneous UIDs or the symbol "*".
UIDs are assigned strictly ascending in the mailbox (refer to
[IMAP], section 2.3.1.1) and UID ranges are as in [IMAP]; in
particular, note that a range of 12:10 is exactly equivalent to
10:12 and refers to the sequence 10,11,12.
This response code is returned in a tagged OK response to the
COPY command.
UIDNOTSTICKY
The selected mailbox is supported by a mail store which does not
support persistent UIDs; that is, UIDVALIDITY will be different
each time the mailbox is selected. Consequently, APPEND or COPY
to this mailbox will not return an APPENDUID or COPYUID response
code.
This response code is returned in an untagged NO response to the
SELECT command.
Note: servers SHOULD NOT have any UIDNOTSTICKY mail stores.
This facility exists to support legacy mail stores in which
it is technically infeasible to support persistant UIDs.
This should be avoided when designing new mail stores.
Example: C: A003 APPEND saved-messages (\Seen) {297}
C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
C: From: Fred Foobar <foobar@example.com>
C: Subject: afternoon meeting
C: To: mooch@example.com
C: Message-Id: <B27397-0100000@example.com>
C: MIME-Version: 1.0
C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
C:
C: Hello Joe, do you think we can meet at 3:30 tomorrow?
C:
S: A003 OK [APPENDUID 38505 3955] APPEND completed
C: A004 COPY 2:4 meeting
S: A004 OK [COPYUID 38505 304,319:320 3956:3958] Done
C: A005 UID COPY 305:310 meeting
S: A005 OK No matching messages, so nothing copied
C: A006 COPY 2 funny
S: A006 OK Done
C: A007 SELECT funny
S: * 1 EXISTS
S: * 1 RECENT
S: * OK [UNSEEN 1] Message 1 is first unseen
S: * OK [UIDVALIDITY 3857529045] Validity session-only
S: * OK [UIDNEXT 2] Predicted next UID
S: * NO [UIDNOTSTICKY] Non-persistent UIDs
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen)] Limited
S: A007 OK [READ-WRITE] SELECT completed
In this example, A003 and A004 demonstrate successful appending and
copying to a mailbox which returns the UIDs assigned to the messages.
A005 is an example in which no messages were copied; this is because
in A003 we see that message 2 had UID 304 and message 3 had UID 319;
therefore UIDs 305 through 310 do not exist (refer to section 2.3.1.1
of [IMAP] for further explanation). A006 is an example of a message
being copied that did not return a COPYUID; and as expected A007
shows that the mail store containing that mailbox does not support
persistent UIDs.
5. Formal Syntax
Formal syntax is defined using ABNF [ABNF], extending the ABNF rules
defined in [IMAP4]. The IMAP4 ABNF should be imported first before
attempting to validate these rules.
append-uid = uniqueid
capability =/ "UIDPLUS"
command-select =/ uid-expunge
resp-code-apnd = "APPENDUID" SP nz-number SP append-uid
resp-code-copy = "COPYUID" SP nz-number SP uid-set SP uid-set
resp-text-code =/ resp-code-apnd / resp-code-copy / "UIDNOTSTICKY"
; incorporated before the expansion rule of
; atom [SP 1*<any TEXT-CHAR except "]">]
; which appears in [IMAP]
uid-expunge = "UID" SP "EXPUNGE" SP sequence-set
uid-set = (uniqueid / uid-range) *("," uid-set)
uid-range = (uniqueid ":" uniqueid)
; two uniquid values and all values between
; these two regards of order.
; Example: 2:4 and 4:2 are equivalent.
Servers which support [MULTIAPPEND] will have the following extension
to the above rules:
append-uid =/ uid-set
Security Considerations
The COPYUID and APPENDUID response codes return information about the
mailbox. These response codes SHOULD NOT be issused if the client
does not have access to SELECT or EXAMINE the mailbox.
IANA Considerations
This document constitutes registration of the UIDPLUS capability in
the imap4-capabilities registry, replacing RFC 2359.
Normative References
[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[IMAP] Crispin, M., "Internet Message Access Protocol -
Version 4rev1", RFC 3501, March 2003.
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[MULTIAPPEND] Crispin, M., "Internet Message Access Protocol (IMAP) -
MULTIAPPEND Extension", RFC 3502, March 2003.
[RFC-2822] Resnick, P., "Internet Message Format", RFC 2822, April
2001.
Informative References
[RFC-2359] Myers, J., "IMAP4 UIDPLUS extension", RFC 2359, June
1988.
Acknowledgements
This document obsoletes [RFC-2359]. However, it is based upon that
document, and takes substantial text from it.
Author's Address
Mark R. Crispin
Networks and Distributed Computing
University of Washington
4545 15th Avenue NE
Seattle, WA 98105-4527
Phone: (206) 543-5762
EMail: MRC@CAC.Washington.EDU
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